Coasts, Volume 1, Issue 1 (December 2021) – 5 articles

Low tide terrace (LLT) beaches are characterised by a moderately steep beach face and a flat shallow terrace influencing the local hydro-morphodynamics during low tide. The upper beachface slope ($\beta$) and the terrace width ($L_t$) are the main morphological parameters that define the shape of LTT cross-shore beach profiles. This work aims at better understanding the behaviour of $\beta$ and $L_t$ and their link with the incoming wave forcing. For this purpose, our results are based on 3.5 years times series of daily beach profiles and wave conditions surveys at two different microtidal LTT beaches with similar sediments size but different wave climate, one at Nha Trang (Vietnam) and the other one at Grand Popo (Benin). While they look similar, two contrasting behaviour were linked to two sub-types of LTT regimes: the first one is surf regulated beaches (SRB) where the swash zone is highly regulated by the surf zone wave energy dissipation on the terrace, and the second is swash regulated beaches (SwRB) acting in more reflective regime where the terrace is not active and the energy dissipation is mainly produced in the swash zone, the terrace becomes a consequences of the high dynamics in the swash zone. Finally, extending the common view of an equilibrium beach profile as a power law of the cross-shore distance, the ability of a simple parametrized cubic function model with the Dean number as unique control parameters is proposed and discussed. This simple model can be used for the understanding of LLT environments but it can not be extended to the whole beach spectrum. Full article

Exploratory statistical partitioning methods (K-means Clustering analysis) were applied to ADCP monitoring datasets collected inside the Douro and Minho estuaries. This analysis is aimed to discriminate ADCP acoustic responses according to the variations of the suspended particles within the ensonified medium. Based on the interpretation of the results, this work establishes general sediment transport patterns at both estuaries’ exits under continuously varying river flows and tidal amplitudes recorded during a summer dry seasonal scenario (September 2005) and winter high river discharge (January/February 2007) conditions. Results confirm the already known present scarcity of (sandy) sediment export from the Douro and Minho estuaries into the inner shelf and the consequent sediment depletion of the adjacent littoral, with no effective contribution of the Douro and some evidence of sand export observed at the Minho outlet during the winter of 2007. Full article

The tidal variability of the Minho and Douro lower estuaries (NW Portugal) water column structure was assessed at the semi-diurnal and fortnightly time scales under two contrasting seasonal river flow scenarios during the summer of 2005 and winter of 2006. Sediment fluxes inferred from calibrated ADCP acoustic backscatter revealed that, during spring tides and low runoff conditions, both estuaries act as sinks instead of sources of sediments into the inner shelf. Sediment export occurred during neaps, in both estuaries, when the river flow values were high enough to counteract the effect of the entering flood. No evidence of coarse sediment export into the inner shelf that would eventually nourish the littoral system could be inferred from these datasets. Full article

The deposition of Posidonia oceanica leaves on the sandy beaches of the Calabrian region could be one of the most important defence mechanisms against erosion processes. The management of Posidonia oceanica leaf litter in Italy has been realised through the mechanical removal and transport in dumping areas of the beach-cast material. This solution, apparently simple and fast, produces a net loss of sediments from sandy beaches and, therefore, a deficit in the sedimentary budget of the coastline, leading the coastal system to possible shore erosions. Instead, it could be better to keep these vegetable deposits in place to warrant a positive sedimentary budget and to increase the tourist value of regional beaches, improving coastal tourism in seaside resorts with opportunities for bathing. Full article

Coastal dunes are valuable and vulnerable habitats that require scientific exploration and understanding of their natural processes; therefore, the aims of this study were to determine the current vegetation characteristics of dune habitats along the Bulgarian Coast in terms of species richness and cover of typical psammophytes and different non-psammophytic plant groups, and to analyze how they respond to certain environmental drivers. Data were collected from 12 dune systems. The research was focused on embryonic, white and grey dunes. The field work was conducted throughout July and August 2017. The vegetation was sampled at 154 phytosociological plots (5 m × 5 m). To understand how the vegetation responds to different drivers, we tested the correlation of defined species group richness and cover in relation to (1) the soil pH and EC values, (2) the distance from inland to the sea and (3) the range of different categories of land cover in the surrounding area. In order to track temporal vegetation changes, we compared the cover of defined species groups between 2003 and 2017. We registered a total number of 269 vascular plants, 12 bryophytes and 5 lichens. The strongest presence in all dune types, both in species richness and cover, was the group of grass- and shrubland plants. Weeds and ruderal plants had significant coverage in grey dunes, while the richness and cover of forest and alien plants were negligible among the studied dune habitats. The comparison of data between 2003 and 2017 revealed a substantial decline in the cover of psammophytes. We observed a clear pattern regarding the share of species richness of psammophytes and non-psammophytes among different locations. We detected that grey dunes were the most affected by the penetration of non-psammophytes. Full article